1. Field of the Invention
The present invention relates to intraocular lenses, and more specifically intraocular lenses having astigmatic correction. More particularly, the present invention relates to an intraocular lens in which the optic can be angularly adjusted relative to the haptics to thereby adjust the axis of astigmatic correction following implantation.
2. State of the Art
The cornea of a perfectly shaped eye has a smooth circular surface, like a sphere. Corneal astigmatism is a common condition in which the eye's cornea has an irregular, oblong shape causing a refractive error resulting in distorted vision. The condition, if requiring treatment, is often treated with corrective lenses such as eyeglasses or contact lens or laser refractive surgery (laser in-situ keratmileusis (LASIK) or photorefractive keratectomy (PRK)).
While corneal astigmatism is often treated with corrective lenses or laser refractive surgery, corneal astigmatic patients having cataracts and undergoing surgery to replace the cataract lens with an intraocular lens (IOL) can request the implantation of a toric intraocular lens adapted to treat their corneal astigmatic condition during their lens replacement surgery. Toric lenses must be implanted along a prescribed rotational axis of correction such that the optical correction designed into a lens is directed along the correct rotational axis to properly treat the distortion. It has been noted that critical to the success of a toric IOL is its rotational stability in the capsular bag; for every degree of misalignment off the desired axis there is a 3 percent loss of cylinder correction. Lane S. et al., The Correction of Astigmatism During Cataract Surgery with Toric Intraocular Lenses, Cataract Surgery, Ch. 39, p. 469-475, Elsevier (Third Ed., 2010). However, not all implantations are successful in achieving the intended rotational alignment. Further, even after a lens has been implanted, there can be an unpredictable degree of rotational shift that occurs during post-operative healing to the capsular remnant which can result in the lens rotating relative to the initial axis of implantation. One study has found that at two weeks post-implantation, at least 38% of the optics had rotated more than 10°, and in some cases had significantly greater rotation off axis. Id. The resulting axial misalignment can reduce or eliminate the desired correction. Moreover, axial misalignment can introduce higher order optical aberrations which are not correctable with glasses.